Dual-element MEMS microphone for mechanical vibration noise cancellation

Abstract

Disclosed are systems, devices, and methods for minimizing mechanical-vibration-induced noise in audio signals. In one aspect, a microphone is disclosed that includes a first backplate, a first diaphragm, a second backplate, and a second diaphragm. The first diaphragm moves relative to the first backplate in response to acoustic pressure waves in an environment and mechanical vibrations of the microphone, thereby causing a first capacitance change between the first diaphragm and the first backplate. The second diaphragm is substantially acoustically isolated from the acoustic pressure waves, and moves relative to the second backplate in response to the mechanical vibrations of the microphone, thereby causing a second capacitance change between the second diaphragm and the second backplate. The microphone further includes or is communicatively coupled to an integrated circuit configured to generate an acoustic signal based on the first capacitance and the second capacitance.

We claim: 
     
       1. An apparatus comprising:
 a microphone; and 
 an integrated circuit, 
 wherein the microphone comprises a first diaphragm arranged such that: (i) the first diaphragm moves, relative to a first backplate, in response to acoustic pressure waves in an environment of the microphone, and (ii) the first diaphragm also moves, relative to the first backplate, in response to mechanical vibrations of the microphone, wherein movement of the first diaphragm relative to the first backplate causes a first capacitance change between the first diaphragm and the first backplate; 
 wherein the microphone further comprises a second diaphragm that is substantially acoustically isolated from the environment of the microphone such that the second diaphragm does not move substantially, relative to a second backplate, in response to the acoustic pressure waves in the environment, wherein the second diaphragm moves, relative to the second backplate, in response to the mechanical vibrations of the microphone, and wherein movement of the second diaphragm relative to the second backplate causes a second capacitance change between the second diaphragm and the second backplate; and 
 wherein the integrated circuit is configured to generate an audio signal based on a difference between the first capacitance change and the second capacitance change. 
 
     
     
       2. The apparatus of  claim 1 , wherein:
 the first capacitance change comprises (i) an acoustic capacitance change based on the movement of the first diaphragm relative to the first backplate in response to the acoustic pressure waves and (ii) a first mechanical capacitance change based on the movement of the first diaphragm relative to the first backplate in response to the mechanical vibrations; 
 the second capacitance change comprises a second mechanical capacitance change based on the movement of the second diaphragm relative to the second backplate in response to the mechanical vibrations; and 
 the first mechanical capacitance change is substantially equal to the second mechanical capacitance change. 
 
     
     
       3. The apparatus of  claim 1 , wherein the integrated circuit being configured to generate the audio signal based on the difference between the first capacitance change and the second capacitance change comprises the integrated circuit being configured to:
 convert the first capacitance change into a first voltage signal, wherein the first voltage signal is based on both the acoustic pressure waves and the mechanical vibrations; 
 convert the second capacitance change into a second voltage signal, wherein the second voltage signal is based on the mechanical vibrations; and 
 subtract the second voltage signal from the first voltage signal to generate an acoustic signal. 
 
     
     
       4. The apparatus of  claim 1 , wherein each of the first diaphragm and the second diaphragm comprises silicon. 
     
     
       5. The apparatus of  claim 1 , wherein each of the first backplate and the second backplate comprises silicon. 
     
     
       6. The apparatus of  claim 1 , further comprising support structures, wherein each of the first diaphragm and the second diaphragm are flexibly mounted to the support structures. 
     
     
       7. The apparatus of  claim 6 , wherein the support structures comprise silicon. 
     
     
       8. The apparatus of  claim 1 , further comprising a substrate, wherein:
 at least the first backplate, the first diaphragm, the second backplate, and the second diaphragm are formed on the substrate; and 
 the substrate comprises an opening configured to receive the acoustic pressure waves. 
 
     
     
       9. The apparatus of  claim 8 , further comprising a lid formed (i) on the substrate and (ii) over at least the first backplate, the first diaphragm, the second backplate, and the second diaphragm. 
     
     
       10. A microphone comprising:
 a first diaphragm that is arranged such that: (i) the first diaphragm moves, relative to a first backplate, in response to acoustic pressure waves in an environment of the microphone, and (ii) the first diaphragm also moves, relative to the first backplate, in response to mechanical vibrations of the microphone, wherein movement of the first diaphragm relative to the first backplate causes a first capacitance change between the first diaphragm and the first backplate; and 
 a second diaphragm that is substantially acoustically isolated from the environment of the microphone such that the second diaphragm does not move substantially, relative to a second backplate, in response to the acoustic pressure waves in the environment, wherein the second diaphragm moves, relative to the second backplate, in response to the mechanical vibrations of the microphone, and wherein movement of the second diaphragm relative to the second backplate causes a second capacitance change between the second diaphragm and the second backplate. 
 
     
     
       11. The microphone of  claim 10 , wherein each of the first diaphragm and the second diaphragm comprises silicon. 
     
     
       12. The microphone of  claim 10 , wherein each of the first rigid backplate and the second rigid backplate comprises silicon. 
     
     
       13. The microphone of  claim 10 , further comprising support structures, wherein each of the first diaphragm and the second diaphragm are flexibly mounted to the support structures. 
     
     
       14. The microphone of  claim 13 , wherein the support structures comprise silicon. 
     
     
       15. The microphone of  claim 10 , wherein the first diaphragm is adjacent to the second rigid backplate. 
     
     
       16. The microphone of  claim 10 , wherein the first rigid backplate is adjacent to the second rigid backplate. 
     
     
       17. The microphone of  claim 10 , wherein the first flexible diaphragm is adjacent to the second flexible diaphragm. 
     
     
       18. The microphone of  claim 10 , wherein the first rigid backplate is adjacent to the second flexible diaphragm. 
     
     
       19. A method comprising:
 determining a first capacitance change between a first diaphragm and a first backplate of a microphone, wherein the first capacitance change is determined based on movement of the first diaphragm relative to the first backplate, and wherein the first diaphragm moves, relative to the first backplate, in response to both acoustic pressure waves in an environment of the microphone and mechanical vibration of the microphone; 
 determining a second capacitance change between a second diaphragm and a second backplate of the microphone, wherein the second capacitance change is determined based on movement of the second diaphragm relative to the second backplate, and wherein the second diaphragm does not substantially move, relative to the second backplate, in response to the acoustic pressure waves in the environment of the microphone but the second diaphragm does move, relative to the second backplate, in response to the mechanical vibration of the microphone; and 
 generating an audio signal based on a difference between the first capacitance change and the second capacitance change. 
 
     
     
       20. The method of  claim 19 , wherein generating the audio signal based on the difference between the first capacitance change and the second capacitance change comprises:
 converting the first capacitance change into a first voltage signal, wherein the first voltage signal is based on both the acoustic pressure waves and the mechanical vibrations; 
 converting the second capacitance change into a second voltage signal, wherein the second voltage signal is based on the mechanical vibrations; and 
 subtracting the second voltage signal from the first voltage signal to generate an acoustic signal.